Sinead's thrilled: "I'm absolutely delighted. I think it's absolutely brilliant! I have all the people who voted for me to thank for this. It's a dream come true!"
It's reported the 22-year-old former waitress will make five albums with Mercury but they haven't confirmed it.
Mercury have already signed fellow wannabes Malachi and Ainslie.
Soul-boy Lemar, who was voted off Fame Academy during the final is reportedly in talks with record bosses as well.